The present invention relates to copying data between storage devices. In particular, the invention relates to a method for sharing bandwidth between multiple remote copy targets.
Peer to Peer Remote Copy (PPRC) is a method to replicate a storage volume to another storage unit over extended distances to a remote site. PPRC is used to provide business continuity and disaster recovery capabilities. A PPRC may be performed synchronously or asynchronously. In Synchronous PPRC, each write to a local site is performed to the remote site as well. The Synchronous PPRC is complete when the write completes to both sites. An example of a Synchronous PPRC implementation is IBM® Metro Mirror (IBM is a registered trademark of International Business Machines Corporation in the United States, other countries, or both.) In Asynchronous PPRC, each write is made to the local site, and then copied to the remote site when time permits. The Asynchronous PPRC is complete when the write completes to the local site. Different copy functions may be combined to provide remote copy functionality. For example, a Point in Time copy may be made at the local site between a source volume and a target volume, and then a remote copy may be made from the target volume to a remote site. An example of a combinatorial implementation is IBM Global Mirror. PPRC may be used to provide very fast data recovery due to failure of the primary site.
PPRC may also be extended to more than one remote site to improve business continuity and disaster recovery capabilities.
If an organisation has three sites, A, B, and C, and wishes to replicate data from a storage system at A onto similar systems at B and C using a PPRC method, a high-bandwidth network connection is required from A to B, and from A to C. An example of a suitable network connection protocol is Fibre Channel (FC). However, FC links are expensive as they are priced by distance and bandwidth.